Charged particle beam apparatuses are used in a plurality of industrial fields. Inspection of semiconductor devices during manufacturing, exposure systems for lithography, detecting devices and testing systems are only some of these fields.
In general, there is a high demand for structuring and inspecting specimens within the micrometer or nanometer scale. On such a small scale, process control, inspection or structuring is often done with charged particle beams, e.g. electron beams, which are generated and focused in charged particle beam devices such as electron microscopes or electron beam pattern generators. Charged particle beams offer superior spatial resolution compared to, e.g. photon beams due to their short wavelengths.
Generally, charged particle beam devices are operated under vacuum conditions to avoid, e.g. ionization of surrounding gases. In spite of that, electrons impinging on component surfaces of the device, like extractors, anodes, apertures or the chamber wall result in an emission of contaminants. This phenomenon is known as electron stimulated desorption (ESD). Thus, a shower of residual gas is generated. The residual gas contains molecules which can be hit by electrons. Thereby, ions, ionized molecules and other particles such as electrons can be created. In the case of particles having a charge which is opposite to the charge of the charged particles emitted by an emitter, the particles in the residual gas are accelerated towards the emitter. As a result, the emitter can be mechanically deformed from the impingement of the ions and ionized molecules or these particles can be deposited on the emitter. Thus, emitter noise is introduced.
Present approaches for pretreatment of the device are not completely satisfactory. For example, in a pretreatment using heating, the thermal energy may be too low to desorb chemically adsorbed particles from the surfaces of the device. Even with a pretreatment making use of ESD, the time needed for pretreatment may be excessively long, e.g. several days to weeks.